JP-2000-170905A (U.S. Pat No. 6,230,576) shows a shift-by-wire system of an auto-transmission. In this system, a shift range selected by a vehicle occupant is detected, and a shift-changing valve for changing the shift range in an automatic transmission is actuated by an actuator such as an electric motor in accordance with the detected shift range.
The shift-by-wire system is provided with a range detector. When a change of the shift range is instructed, an electric current is supplied to an electric motor until an actual shift range detected by the shift range detector becomes coincident with the instructed shift range. According to such a system, however, upon occurrence of a trouble of the range detector such as, for example, failure of the range detector itself, disconnection of a harness for connection between the range detector and a controller in the shift-by-wire system, or a short-circuit of the harness, it becomes no longer possible to detect an actual shift range and hence impossible to make switching to the instructed shift range.